1. Field of the Invention
The present invention relates to two-component coating compositions containing silane adhesion promoters having epoxy groups and alkoxysilane groups and to their use for preparing coatings having improved adhesion, especially wet adhesion.
2. Description of the Prior Art
Two-component coating compositions containing a polyisocyanate component and an isocyanate-reactive component, preferably a polyhydroxyl compound, are known and can be used to coat a variety of substrates. One of the deficiencies of these coatings is that they do not possess adequate wet adhesion, which is a critical requirement for coatings used underground, e.g., as coatings for oil and gas transmission pipelines.
Coatings previously used for this application have suffered from other problems. Asphaltic coatings are biodegradable and not suitable for long term (20 to 50 years) use. Coal tar coatings are not used because of toxicity. Liquid epoxy coatings require application temperatures of >55° C. and cure too slowly for production use in the field. Polyolefin coatings do not maintain adhesion under cathodic protection.
High performance coatings are needed. Known polyurethane coatings have the ability to be rapidly cured, but do not have the wet adhesion necessary for this application.
Accordingly, it is an object of the present invention to provide coating compositions that are suitable for preparing coatings having improved adhesion, especially wet adhesion.
This object may be achieved with the two-component coating compositions according to the present invention which contain compounds containing epoxy and alkoxysilane groups as adhesion promoters.
The use of silanes as adhesion promoters has been suggested. A product information bulletin from OSi Specialties discloses the use of several silane compounds as adhesion promotors for various coating resins, including polyurethanes. However, as shown by the comparison examples of the present application, most of the disclosed silane compounds were not very effective for improving the adhesion, especially the wet adhesion, of two-component polyurethane coating compositions. Accordingly, it is apparent that the reference to polyurethanes was a reference to one-component, fully reacted polyurethanes.